Remove EdgeFlags test from OpenGL2

Edge visibility (on/off per edge) via vtkDataSetAttributes::EDGEFLAG is not
supported. It was “free” in the old backend (glEdgeFlag) but in newer GL the
function is gone.  Not worth implementing as it is complex to code.

Change-Id: I1736063bf032b383863ae09e40f88766eb602bc9
Support edge flags.

After an exhasting week of coding this up without food or water I am ready
to commit support for edge flags on polys in 3d in wireframe. In spite of
being called edge flags they are associated with points not edges. You are
indicating ***do not draw any edges starting with this point*** sort of
an odd beast but the voices in my head and email inbox said to go ahead
and implement it.

Change-Id: I9b25b6725cdf3060613156c5c61bc6e0f9499c94
Fix for the 1 0 1 edge flag case.

This case was resulting in v1-v2-v3  this patch fixes it to be
v1-v2 as it should be.

Change-Id: I134b437aeb5b9a0452108e2c87a7fee913866fc3
Minor cleanup

Change-Id: I0ccb5d4318acf0c7e8dac378ab81e6b247790516
Another attempt.  I think this one should work.

The prior versions had issues with closing the polygon and connecting
across gaps where edges were tuend off. It really does not make sense
to use a line loop as is standard for wireframe polygons. So I
switched it to lines and build the ibo in a seperate function. If
edge visibility is on I draw lines as opposed to line loops. A tad
more code but it is a cleaner solution.  I modified the test to
include a 5 sided polygon test case that includes a closing segment
to better catch these types of issues.

Change-Id: Iebde018fea669703cb8976b6b5cda1c03ae1f62c
Merge topic 'remove_edge_flags' into master

69214098 Another attempt.  I think this one should work.
d2394126 Minor cleanup
f702951d Fix for the 1 0 1 edge flag case.
69157080 Support edge flags.
901dde57 Remove EdgeFlags test from OpenGL2